The present invention relates to a high capacity data communication network and to a network node suitable for the same.
In both local (LAN) and metropolitan (MAN) area data communication networks, one of the factors to be taken into account in evaluating the communication protocol, is the possibility of a fair sharing of the communication medium capacity among the network nodes.
For a metropolitan area network a protocol, known as DQDB (Distributed Queueing Dual Bus), has been standardized by the IEEE 802.6 working group; for a detailed description of such protocol one may refer, e.g., to the book of Martin De Prycker titled "Asynchronous Transfer Mode: solution for Broadband ISDN", London, Ellis Horwood, November 1990, para. 6.5 "DQDB", pages 246 to 255.
Such a protocol is based upon a dual bus architecture, in which there are two network nodes that act also as head-end stations generating and erasing slots over and from the network, and in which all the network nodes transmit by capturing the free slots. One of the well known problems of such protocol is the "unfairness", i.e. the fact that some nodes of the network are favoured with respect to the others, more precisely: the nearer a node has a position on the bus close to the head-end station, the greater the probability of capturing a free slot will be; such advantage is reduced by the fact that the DQDB protocol has a slot-reserving mechanism.
Several solutions to this problem are known from the literature; for a short review see, e.g., P. Davids et al., "Performance enhancement in DQDB networks", Proceedings EFOC/LAN '92, pages 223 to 228, Paris, 24-26/06/92; such solutions do not solve totally the problem; moreover they are not always easily and economically implementable.
The data communication networks, in particular the metropolitan area networks, are nowadays requiring a higher and higher capacity in terms of traffic transportation.
Several solutions have been proposed using optical fibers and WDM (Wavelength Division Multiplex) technique, among which the parallel architecture based on DQDB protocol set forth by S. Casale et al. in "A PARALLEL ARCHITECTURE FOR A DQDB MAN", Proceedings ICCC '92 pages 415 to 419, Genoa, 28/10/1992, is of particular interest.
Also this parallel architecture has the problem of "unfairness" since it is composed of a plurality of dual buses all connected to the various nodes and using the DQDB protocol.